JP4632363B2 - Magnetic field generating coil - Google Patents

Description

  The present invention relates to a magnetic field generating coil used in automobiles, home appliances, communication equipment, ships, aircraft, medical equipment and the like.

  A magnetic field generating coil is formed by winding a conductor wire such as a copper wire around a cylindrical or similar polyhedral tube and applying a voltage to the conductor wire, so that an electric current flows along the conductor wire. It is a coil that generates a magnetic field around it in accordance with the circuit law.

  In various uses, a magnetic field generating coil is required to be uniform, and a conventional magnetic field generating coil with improved magnetic field uniformity includes a split type magnetic field generator for MRI. A pair of coils in a split type MRI magnetic field generator facing a magnetic pole device having a coil assembly having a plurality of annular coils and a coil storage container for storing the assembly, and arranged with a predetermined space interval The magnetic field in the space between is uniformly controlled.

  Patent Document 2 uses a small-diameter coil and a large-diameter coil, a first coil assembly for generating a main magnetic field in a predetermined region, and a second for generating a magnetic field for shielding a leakage magnetic field leaking from the main magnetic field. There are MRI systems with coil assemblies that provide a high uniform magnetic field. The large-diameter coil generates a zero magnetic field of approximately 5% of the combined magnetic field at the center of a predetermined region, and can be used to control the width of the uniform space to be about twice when used in combination with a magnet.

  Non-Patent Document 1 describes a pair or two pairs of the same large ring (helmholtz coil system) facing each other. In this method, a uniform magnetic field region is provided in the central region of the opposing coil.

JP-A-10-99296 JP-A-8-288120 Magnetic engineering, Yoshii Yoshii, Kaibundo Publishing 1969, p95-.

  The internal generated magnetic field of a normal solenoid coil is a uniform magnetic field at the center of the coil, but as it goes to the end of the coil, the magnetic field is not uniform due to the influence of the demagnetizing field, and the generated magnetic field in the axial direction is attenuated. In order to increase the uniformity of the generated magnetic field inside the coil, means for opposing two coils and providing a uniform magnetic field range at the center of the opposed coils is known as the Helmholtz coil system. The Helmholtz coil system provides a uniform magnetic field region in the space between coils, and the magnetic field increases near the center of one coil, and the magnetic field can be made uniform up to the coil end. There is no problem.

  In this situation, an object of the present invention is to provide a magnetic field generating coil in which an axial magnetic field is uniform along the coil center line to the coil end.

In order to solve the above-mentioned problems, a magnetic field generating coil according to the present invention is a magnetic field generating coil composed of a multi-layered laminated solenoid coil wound with a conductive wire. The diameter of the conducting wire wound at the coil end is made thinner than the coil center so that the coil winding cross-sectional area at the coil end becomes smaller than the coil center. And

  The laminated solenoid coil has a divided structure divided in the length direction, and changes the number of windings of the conductive wire wound around each divided bobbin so that the number of windings at the bobbin located at the center is at the end. It is preferable to increase the number of turns of the bobbin located.

  When the coil winding cross-sectional area is changed by changing not only the number of turns of the conductor wound around the divided bobbin but also the diameter of the conductor to be wound for each bobbin, the number of turns increases at the coil end. Also, an increase in coil winding cross-sectional area can be suppressed.

  As described above, according to the present invention, the coil in the magnetic field generating coil is divided and wound, and the winding diameter of the divided coil at the end is reduced, so that the number of turns is increased as compared with the coil near the coil center. However, a structure in which the outer diameter of the winding is reduced can provide a magnetic field generating coil having a wide uniform magnetic field region in which the attenuation of the axial magnetic field from the coil center to the end is corrected.

  Next, the magnetic field generating coil in the embodiment of the present invention will be described. In the first embodiment of the present invention, the number of turns of the parallel densely wound laminated solenoid coil is gradually increased from the coil center to the coil end of the parallel densely wound laminated solenoid coil wound by the conductive wire. By doing so, a magnetic field generating coil having a magnetic field uniformity in which the magnetic field inside the coil is suppressed to 1% or less of the magnetic field attenuation at the coil end portion with respect to the coil center portion can be obtained.

  In the second embodiment of the present invention, the laminated solenoid coil has a divided structure in which the entire length of the solenoid is divided into several parts, and the number of turns of the coil wound around each divided bobbin is changed. A bobbin in the vicinity of both ends within at least 1/10 of the total number of turns of the bobbin at the center of the coil is a magnetic field generating coil having a bobbin with an increased number of turns.

  In the third embodiment of the present invention, the laminated solenoid coil suppresses an increase in coil winding cross-sectional area by changing not only the number of times of the divided bobbin windings but also the diameter of the wire to be wound. Yes. In order to explain the action at that time, the expression for the cylindrical solenoid coil when the internally generated magnetic field is H is expressed as follows: number of turns N, applied current I, coil length l, coil inner diameter a, coil outer diameter b, coil axial direction The coordinate x is shown in Equation 1.

  Thus, the internally generated magnetic field H can be increased by reducing the difference between the coil inner diameter a and the coil outer diameter b. That is, in the vicinity of the end portion, although the number of turns N is increased, the physical outer diameter is suppressed, and the coil winding cross-sectional area is not increased with respect to the coil outer diameter on the coil center side. A magnetic field generating coil with improved uniformity can be obtained.

  Even if the number of turns of each of the divided bobbins is constant, the axial magnetic field can be reduced by gradually decreasing the coil winding cross-sectional area from the coil center to the coil end (opening). A magnetic field generating coil with improved uniformity can be obtained.

  Hereinafter, a magnetic field generating coil according to an embodiment of the present invention will be described with reference to the drawings. First, a comparative example manufactured before reaching the present invention will be described.

(Comparative Example 1) The magnetic field generating coil of Comparative Example 1 using a general solenoid coil was closely wound in parallel with a copper wire in a quadrangular prism shape, and wound while being laminated.

  FIG. 1 is a perspective view showing a magnetic field generating coil of Comparative Example 1, and a polyurethane-coated copper wire 102 of φ0.12 mm is tightly wound in parallel on a bobbin 101 having an outer width of 31.6 mm × height of 7.6 mm × length of 33 mm. The laminated solenoid coil is wound 229 times per layer and wound 687 times in three layers. The shaded part is a part related to the microstrip line substrate to which a magnetic field is applied.

  A DC current of 10 mA was passed between the start and end of winding of the wound wire. The magnetic field in the axial direction at the center inside the coil was measured using a Gauss meter using a Hall element and a fluxgate type magnetic sensor.

  An axial magnetic field Hy = 636.6 [A / m] (8.0 [Oe]) is generated at the coil center. FIG. 2 shows the magnetic field distribution in the axial direction near the center plane inside the coil. Here, 10 represents the entire outer shape of the magnetic field generating coil. The coil ends are attenuated to 573 [A / m] (7.2 [Oe]) or less. FIG. 3 is a graph showing the magnetic field distribution up to the coil end with the coil center as the reference magnetic field from the numerical data. The axial magnetic field Hy at the end portion is 27% lower than the axial magnetic field Hy at the center of the coil.

  (Comparative Example 2) In order to suppress a rapid magnetic field attenuation from the coil center to the coil end as shown in FIG. 3, the magnetic field generating coil of the comparative example 2 using the Helmholtz coil is formed into two square ring coils. It was produced by winding in parallel with a copper wire and winding while laminating.

  FIG. 4 is a perspective view showing the magnetic field generating coil of the second comparative example. One layer of a polyurethane-coated copper wire 103 having a diameter of 0.12 mm is provided on a bobbin 101 having the same size as that of the first comparative example and within a range of 11 mm from the end of the coil. This is a Helmholtz coil with a total of 760 turns at both ends of the coil. The shaded part is a part related to the microstrip line substrate to which a magnetic field is applied.

  An axial magnetic field Hy = 250.7 [A / m] (3.15 [Oe]) is obtained at the coil center at the same DC current of 10 mA as in Comparative Example 1. Since the coil is concentrated and wound only at the end portion, the axial magnetic field Hy is about 2.5 times as large as the coil center magnetic field just below the coil end portion. FIG. 5 shows a graph of numerical data similar to that of FIG. That is, FIG. 5 is a view showing the magnetic field distribution in the axial direction near the center plane inside the coil of Comparative Example 2. FIG. 6 is a diagram showing the magnetic field distribution up to the coil end with the coil center as the reference magnetic field.

  (Embodiment 1) FIG. 7 is a perspective view showing a magnetic field generating coil in Embodiment 1 of the present invention. In the present invention, the coil length is divided into 11 pieces as shown in FIG. Each bobbin at the center was wound with 110 to 120 times of a polyurethane-coated copper wire having a diameter of 0.18 mm. Further, a bobbin at the end (opening) was manufactured by winding 225 times. By connecting the bobbins in series, a finite-length solenoid coil is formed, and in order to expand the coil axial direction uniform magnetic field region in the coil width direction, the width direction is from 31.6 mm of Comparative Example 1 and Comparative Example 2. The coil width was increased to 61.6 mm to obtain the structure shown in FIG. The shaded portion is a portion related to the terminal treatment of the microstrip line substrate to which the magnetic field is applied and the magnetic field generating coil copper wire. The divided coil 104 sets the number of turns of the bobbin located at the center of the whole to 110 times, sets the number of turns of the second bobbin from the coil end (opening) to 120 times, and ends the coil 105 located at the coil end. The number of turns was increased to 225 times. The core wire diameter of the polyurethane-coated copper wire used at that time is φ0.18 mm for the central part of the number of windings 110 and 120, and φ0.12 mm for the end part of the winding number of 225. Even if the number of turns is increased to correct the attenuation, if the difference between the inner and outer diameters of the coil increases, the magnetic field inside the coil does not increase significantly as shown in equation (1). By reducing the winding diameter so as not to increase the difference, a uniform magnetic field can be obtained in the axial direction. That is, the magnetic field uniformity was improved by not increasing the coil winding cross-sectional area in the vicinity of the end (the cross-sectional area of the coil conductor in the plane including the coil central axis).

  FIG. 8 shows the magnetic field distribution in the vicinity of the inner center plane of the magnetic field generating coil according to the first embodiment. FIG. 8A shows a first prototype and FIG. 8B shows a second prototype.

  FIG. 9 is a diagram showing the axial magnetic field distribution up to the coil end in comparison with Example 1 of the present invention and another comparative example with the coil center as the reference magnetic field. Reference numeral 2 denotes a magnetic field distribution of a parallel closely wound solenoid type (Comparative Example 1), reference numeral 3 denotes a Helmholtz type (Comparative Example 2) magnetic field distribution, reference numeral 4 denotes a magnetic field distribution of Example 1 of the present invention, and reference numeral 5 denotes Comparative Example 1. The magnetic field distribution when the parallel dense winding is replaced with divided winding is shown.

  As shown in FIG. 9, in the present invention, the magnetic field uniformity in the axial direction is remarkable. Further, comparing the magnetic field distributions of reference numerals 2 and 5, it can be seen that the magnetic field uniformity is better in the split winding than in the parallel dense winding. Such a magnetic field generating coil of this embodiment is particularly suitable for generating a uniform bias magnetic field inside the magnetic sensor.

The perspective view which shows the magnetic field generation coil of the comparative example 1. FIG. The axial magnetic field distribution map in the vicinity of the center plane inside the coil in Comparative Example 1. The figure which shows the magnetic field distribution to the coil edge part with respect to the reference magnetic field of the coil center in the comparative example 1. The perspective view which shows the magnetic field generation coil of the comparative example 2. FIG. The magnetic field distribution figure of the axial direction in the vicinity of the center surface inside the coil of the comparative example 2. The figure which shows the magnetic field distribution to the coil edge part with respect to the reference magnetic field of the coil center in the comparative example 2. FIG. 3 is a perspective view showing a magnetic field generating coil in Embodiment 1. FIG. 8A shows the magnetic field distribution in the vicinity of the inner central plane of the magnetic field generating coil in Example 1, FIG. 8A is the magnetic field distribution diagram of the first prototype, and FIG. 8B is the magnetic field distribution diagram of the prototype. The figure which shows the distribution of the axial direction magnetic field to a coil edge part by making a coil center into a reference magnetic field by contrast in Example 1 of this invention, and another comparative example.

Explanation of symbols

2, 3, 4, 5 Magnetic field distribution 10 Overall outline of magnetic field generating coil 101 Bobbin
102,103 polyurethane coated copper wire
104 Split coil 105 End coil Hy Axial magnetic field

Claims (2)

In a magnetic field generating coil comprising a multi-layered laminated solenoid coil wound with a conducting wire, the number of windings of the conducting wire at the coil end is increased more than the coil center, and the coil at the coil end rather than the coil center. A magnetic field generating coil characterized in that a diameter of a conducting wire wound at an end of the coil is made thinner than a central portion of the coil so that a winding cross-sectional area becomes small .   The laminated solenoid coil has a divided structure divided in the length direction, and changes the number of windings of the conductive wire wound around each divided bobbin so that the number of windings at the bobbin located at the center is at the end. The magnetic field generating coil according to claim 1, wherein the number of turns on the bobbin located is large.

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